Approaching The Perception Of Touch In The Brain

Over ten percent of the cerebral cortex is involved in dealing with information about the sense of touch — a larger area than previously thought – according to a joint study by researchers from the Max Planck Institute for Human Cognitive and Brain Sciences in Leipzig and Ruhr Universität Bochum.

An encouraging pat on the back or a soft sweater on the skin — even things that we do not actively explore with the hands, we perceive with our body perception.

“Which brain areas are responsible for this perception of touch, however, is still largely unknown,”

says Dr. Burkhard Pleger, neurologist at the Berufsgenossenschaftlichen Kliniken Bergmannsheil in Bochum and co-author of the study. To investigate this question, he and his colleagues from Leipzig examined the brains of 70 patients using structural magnetic resonance imaging (MRI).

Virtual Lesion Symptom Mapping

As the result of an injury or a stroke, participants suffered from a disturbed body perception, such as hypoesthesia — a condition in which the pressure and touch perception of the skin is impaired. People who have suffered such damages — called lesions — in the brain are a particularly important group of patients for neuroscientists.

By comparing the location of the damage in the brain and the symptoms of the patients with each other, the researchers can draw conclusions about the function of individual brain areas, a technique called virtual lesion-symptom mapping (VLSM).

Shown are pairs of the summed lesion maps across patients with and without spatial neglect, superimposed on axial structural T1-weighted MRI images.

Pairs of the summed lesion maps across patients with and without spatial neglect, superimposed on axial structural T1-weighted MRI images.
Credit: M. Rullmann et al, CC-BY

The scientists identified different areas that were linked to a limited sense of touch. In doing so, they were able to support some findings from a previous lesion study on body awareness and also to find new areas of the brain that had not been associated with the perception of touch before.

More Complexity

The researchers were able to show that not only the somatosensory cortex is involved in the perception of touch, but also parts of the prefrontal cortex and posterior parietal lobe — brain regions that are known to be essential for attention-focusing and body awareness.

“The study shows that the brain network responsible for the perception of skin contact is much more complex than previously thought,”

says Pleger.

The study involved 35 patients with brain lesions in the left hemisphere and 35 patients with lesions in the right hemisphere. The resulting findings are in agreement with intracerebral recordings in humans showing that more than 10% of the cortical surface appears to be involved in the processing of somatosensory stimuli.

[1] Rullmann, M., Preusser, S. & Pleger, B. Prefrontal and posterior parietal contributions to the perceptual awareness of touch. Sci Rep 9, 16981 (2019) doi:10.1038/s41598-019-53637-w